This disclosure relates to a fan nacelle for a gas turbine engine and an associated flow control device.
Gas turbine engines for commercial aircraft applications typically include an engine core housed within a core nacelle. In one type of arrangement known as a turbofan engine, the core drives a large fan upstream from the core that provides airflow into the core. A significant portion of airflow bypasses the core to provide thrust. One or more spools are arranged within the core, and a gear train may be provided between one of the spools and the fan. A fan case and fan nacelle surround the fan and at least a portion of the core.
The performance of a turbofan engine varies during diversified conditions experienced by the aircraft. An inlet lip portion located at the foremost end of the fan nacelle is typically designed to enable operation of the turbofan engine and reduce the separation of airflow from the inlet lip of the nacelle assembly during these diversified conditions. For example, the inlet lip requires a “thick” inlet lip to support operation of the engine during specific flight conditions, such as cross-wind conditions, take-off and the like. Disadvantageously, the thick inlet lip may reduce the efficiency of the turbofan engine during normal cruise conditions of the aircraft. As a result, the maximum diameter of the fan nacelle may be approximately 10-20% larger than required during cruise conditions.
In addition, boundary layer separation is a common problem associated with thick inlet lip. Boundary layer separation occurs where airflow communicated through the inlet lip separates from an inner surface of the inlet lip portion, which may cause engine stall, the loss of the capability to generate lift, and may decrease engine efficiency.
One suggested approach to reducing the inlet lip thickness is to provide a flexible inlet that can be deflected to a desired shape to prevent boundary layer separation. Another suggested approach is to deploy structure exteriorly of the fan nacelle to affect the boundary layer flow. In addition, synthetic jets are known which introduce an airflow at the boundary layer to increase the velocity gradient of the oncoming airflow near the boundary separation point. However, these attempts are potentially complex and expensive or intrude into the space exterior of the fan nacelle thereby adding to the overall engine size.
Accordingly, it is desirable to improve the performance of a turbofan gas turbine engine during diversified conditions to provide a fan nacelle having a reduced thickness, reduced weight and reduced drag.